Gas sensing properties of single-wall carbon nanotubes dispersed with dimethylformamide

For NO₂ gas sensing, we deposited single-walled carbon nanotubes (SWCNTs) on a pair of interdigitated electrodes (IDEs) by using a simple casting method. In order to achieve well-dispersed SWCNTs, we dispersed the as-grown SWCNT powder into dimethylformamide (DMF). We selected DMF as one of the candidate materials to ravel the entangled SWCNT bundles because the amide group could easily attach to the surface of the nanotubes. The resultant SWCNTs were well separated. However, the SWCNTs dispersed in DMF required a heat treatment to eliminate the DMF molecules adsorbed on the surface of the SWCNTs. Therefore, we heated the SWCNTs on the IDEs to 350 °C for 1, 2, 3, and 5 h, to remove the outer DMF adsorbed layers. The assembled sensors were exposed to NO₂ of 3 and 10 ppm concentrations. We attributed the NO₂ gas sensing to the direct charge transfer from the physically adsorbed molecules to the individual p-type semiconducting SWCNTs.